A yarn over is a very simple and decorative increase. The type of yarn over that is performed depends on the stitch that is worked before and after the yarn over.
Yarn Over (YO): Worked Between Two Knit Stitches (as in k1, yo, k1)
1. After working a knit stitch, move the yarn to the front and place it over the top of the right needle.
2. Knit the next stitch.
Yarn Around Needle (YRN): Worked Between Two Purl Stitches (as in p1, yo, p1)
1. After working a purl stitch, move the yarn to the front and wrap it around the right needle brining it over the top of the needle and back to the front.
2. Purl the next stitch.
Yarn Over Needle (YON) – Worked Between a Purl and a Knit Stitch
1. After working a purl stitch, move the yarn to the front and place it over the top of the right needle.
2. Knit the next stitch.